Cliorismia rustica, a new stiletto fly species for Sweden Kevin C. Holston

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Ent. Tidskr. 138 (2017) A new stiletto fly for Sweden

Cliorismia rustica, a new stiletto fly species for Sweden

Kevin C. Holston

Holston, K.C.: Cliorismia rustica, a new stiletto fly species for Sweden. [Cliorismia rus- tica, en ny stilettflugeart för Sverige.] – Entomologisk Tidskrift 138(1): 33-36. Uppsala, Sweden 2017. ISSN 0013-886x.

This paper reports Cliorismia rustica (Panzer, 1804) (Therevidae: Diptera) as a new spe- cies record for the Swedish stiletto fly fauna. In the UK, C. rustica is a notable species listed on the Biodiversity Action Plan and is associated with the conservation priority habitat category Exposed Riverine Sediments. The collecting localities for C. rustica in Sweden are at the Lagan River, in an area characterized by slow-flowing meandering stretches bordered by coniferous-mixed forest. Verified occurences of the genus in Sweden consist of a few records of the other European species of this genus, Cliorismia ardea (Fabricius), from Gotland. On the Swedish Red List, C. ardea (“blekbent vedstilettfluga”) is listed with the status of “Vulnerable” and has been re-collected on Gotland after 90 years. Discovery of C. rustica at this high biodiversity value locality in central Småland is also a reminder that substantial gains in our knowledge of the Diptera fauna can come from targeted sampling of habitats and species in Sweden.

Kevin C. Holston, Naturhistoriska riksmuseet, Box 50007, SE-104 05, Stockholm, Sweden.

E-mail: kevin.holston@nrm.se

sand dune insect survey on Gotland (Johansson 2013).

Country-level checklists are broadly overlap- ping (Lyneborg 1989), but relative abundance and distribution overlap for the two species of European Cliorismia, especially at the landscape scale, remain poorly understood. In Belgium, C.

ardea is considered a “common” species of in- land Flanders, associated with open areas rather than woodland, in contrast to the “very rare” C.

rustica, collected only in 1936 from the Munte area (Grootaert et al. 2001). In general, histori- cal published records of species occurrences are questionable due to taxonomic misidentifications and name misattributions (Lyneborg 1968). Nei- ther Cliorismia species appears on recent Fin- land checklists although both species have been reported for the Saint Petersburg area, Russia (Haarto & Winqvist 2006, Kahanpää et al. 2014).

Only C. rustica has been recorded for Denmark, Lithuania and the UK, but both Cliorismia spe- cies are reported from other northern and central In 2010, a female stiletto fly specimen identi-

fied in the field as Cliorismia was collected at

the Lagan River in Småland, SSE of Skillinga-

ryd. The section of the Lagan where this speci-

men was collected, “Lagan (mellan)”, has high

biodiversity value that can be attributed to the

unaltered riverbed and shoreline substrate com-

position (Carlsson & Liliegren 2005). It is domi-

nated by slow-flowing meandering stretches, is

bordered by coniferous-mixed forest, and has

a sand bottom substrate (Carlsson & Liliegren

2005). Subsequent visits to this area yielded four

additional specimens of this species, Cliorismia

rustica (Panzer), a new species for the Swedish

Diptera fauna. Prior to 2010, Swedish specimens

of Cliorismia in public collections were of the

other European species of this genus, Cliorismia

ardea (Fabricius). Furthermore, all confirmed

localities for Cliorismia in Sweden were on Got-

land and reference collecting events before 1925

(Andersson & Cederberg 2007), with the notable

exception of specimens from a recent coastal

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Ent. Tidskr. 138 (2017) Kevin C. Holston

European countries (Lyneborg 1989, Lutovino- vas et al. 2003). In the UK, C. rustica is listed on the Biodiversity Action Plan (BAP) with action categories covering site discovery and monitor- ing as well as “research into ecological require- ments” (BRIG 2007).

It is difficult to distinguish females of C.

ardea from C. rustica (Stubbs & Drake 2001), both of which have a similar abdominal vesti- ture pattern that is unlike the uniform silvery grey abdomen of males (Fig. 1). Comparative material at the Swedish Museum of Natural

History, Stockholm (NHRS), and published de- scriptions were used to identify female Lagan River specimens as C. rustica as opposed to C.

ardea, the smaller species with less extensive dark regions on abdominal tergites 2-3 (Ly- neborg 1968). Malaise traps are widely-used, effective sampling methods for adult stiletto flies (Holston 2005), but it was very useful to have Lagan River specimens that were collected by hand so vestiture patterns were undamaged.

Male genitalia morphology, redescribed and/or illustrated in several publications, provides un-

Figure 1. Cliorismia rustica (Panzer),

– a) male in lateral view of, NHRS-DIPT000019207, – b) female in lateral veiw, NHRS-DIPT000019208;

– c) female in dorsal view, NHRS-DIPT000019208.

Scale denote millimiters.

Cliorismia rustica (Panzer) – a) hane från sidan, – b) hona från sidan, – c) hona från ovan.

Skalorna visar millimetrar.

a b

c

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Ent. Tidskr. 138 (2017) A new stiletto fly for Sweden

ambiguous characters for identifying C. rustica.

In particular, the distiphallus, which can be seen in pinned and imperfectly preserved specimens, is long and S-shaped in C. rustica whereas it is short and only slightly recurved in C. ardea (Ly- neborg 1968, Weinberg 1985, Stubbs & Drake 2001, Haarto & Winqvist 2006). Cliorismia can be distinguished from similar stiletto fly genera Dichoglena, Pandivirilia, Psilocephala, and Spiriverpa by the presence of hairs on the pro- sternum (Lyneborg 1986). Among the European genera with hairs on the prosternum, Cliorismia lacks parafacial hairs, unlike Acrosathe and Thereva, and both sexes of Dialineura have a strongly dilated antennal scape.

The five Lagan River specimens of C. rus- tica were collected from the leaves of trees and herbaceous vegetation at or near the riverbank (Fig. 4). Sweden: Småland 1.5 km SSE Skill- ingaryd, Lagan River, 57.41147° N, 14.10585°

E, forest undergrowth – 2010.VII.31 (K.C.

Holston), female, NHRS-DIPT000019206; 1.5 km SSE Skillingaryd, Lagan River, 57.41210°

N, 14.10534° E, riverbank vegetation – 2010.VIII.01 (K.C. Holston) male, NHRS- DIPT000019207 – 2011.VIII.03 (K.C. Holston) male, NHRS-DIPT000019208 – 2011.VIII.04 (K.C. Holston) female, NHRS-DIPT000019209 – 2015.VIII.09 (K.C. Holston) male, NHRS- DIPT000019210. Males of C. rustica were found on or near alder trees growing at the river- bank, collected from leaves exposed to sunlight.

Although the availability of substrates in which larvae can develop is considered a main predic- tor of stiletto fly occurrences (Holston 2005), it is worth noting that specimens of C. ardea were similarly associated with alder at Gotland lo- calities where the species was collected recently (Johansson 2013).

The new record for C. rustica is a reminder that the stiletto fly fauna of Sweden may be bet- ter known than in other countries in Europe, but much remains unknown. Considering the gains from surveys and inventories in the UK, such as those for C. rustica and other Exposed River- ine Sediments (ERS) Diptera (Hewitt & Parker

Figure 2. Riverbank veg-

etation at the Lagan River, SSE of Skillinga- ryd, where specimens of C. rustica (Panzer) were collected. (Photo: 2010.

VIII.01, K.C. Holston).

Ån Lagan i Halland, Skill- ingaryd, där C. rustica hit- tades i Sverige för första gången.

Figure 1. Cliorismia rustica (Panzer),

– a) male in lateral view of, NHRS-DIPT000019207, – b) female in lateral veiw, NHRS-DIPT000019208;

– c) female in dorsal view, NHRS-DIPT000019208.

Scale denote millimiters.

Cliorismia rustica (Panzer) – a) hane från sidan, – b) hona från sidan, – c) hona från ovan.

Skalorna visar millimetrar.

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Ent. Tidskr. 138 (2017) Kevin C. Holston

2008a, Hewitt & Parker 2008b, Littlewood &

Stockan 2013), this discovery is also a reminder that substantial gains can come from targeted sampling of habitats and species. A method that was extremely effective for establishing pres- ence of C. rustica during these UK surveys was collecting and rearing stiletto fly larvae, which could be replicated for ERS sites on the Lagan River.

New locality records and ecological observa- tions for Cliorismia species will be important for ongoing national biodiversity and conservation assessments in Sweden. Criterion B (ArtData- banken 2015) categorizes the geographic area covered by a species distribution and was used to assign C. ardea (“blekbent vedstilettfluga”) the status of “Vulnerable” for the Swedish Red List (ArtDatabanken 2015). Although there may be populations of C. ardea at localities away from the seacoast (Johansson 2013), inventories for C. rustica in the UK suggest that Criterion B, with an emphasis on rarity of suitable habi- tats, may be relevant to the conservation of both Cliorismia species in Sweden.

References

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Cliorismia rustica, a new stiletto fly species for Sweden Kevin C. Holston

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